A standard drill chuck has a chuck body rotatable about a chuck axis and formed with a plurality of axially forwardly open and angled guide passages and with a radially outwardly open groove, respective jaws slidable in the passages and each having a row of radially directed teeth and an axially backwardly directed face, and a ring received in the groove and rotatable about the axis relative to the chuck. The ring is formed with a screwthread meshing with the jaw teeth so that rotation of the ring in one direction moves the jaws axially forward and radially together and opposite rotation moves the jaws axially backward and radially apart.
The problem with such a structure is that when the jaws are moved into an extreme rear position they can wedge tightly against the ring and make it very difficult, when they need to be advanced again, to dislodge them. This is particularly likely to happen in a keyless power drill where the standard procedure is to grip an adjustment sleeve mounted on the ring and operate the drill in the appropriate direction to retract the jaws, as in this case the chuck body is rotating relative to the ring at a high rate of speed so that the above-described wedging action is particularly great.